Compression-ignition direct-injection (CIDI) engines employ direct injection of high-velocity jets of fuel into the engine cylinder, where it combusts as it mixes with air. One of the major problems with CIDI engines is the production of unwanted pollutants such as soot and NOx in the in-cylinder combustion process. Previous research results have shown that combustion of incompletely mixed fuel/air in the high-speed injected jets is an important factor in pollutant production. Increasing air entrainment and fuel/air mixing in the injected fuel jets is therefore desirable to reduce engine pollutant production.